This is not really a problem, but an annoyance, as it fills up your logs. This is a known problem for more than years, but has never been corrected (neither by Asterisk nor by Cirpack devs). The usual correction was to add the following line to your startup scripts (/etc/rc.local on Debian for example):iptables -A INPUT -p udp -m udp --dport 5060 -m string --string "Cirpack KeepAlive Packet" -j DROP

But the syntax has changed in iptables, and you’ll get the error:iptables v1.3.6: STRING match: You must specify `--algo'